1. Technical Field
The present disclosure relates to a control device for a vehicle and, in particular, relates to a control device for a vehicle including an engine, a continuously variable transmission (CVT), and a lock-up clutch.
2. Description of Related Art
As a transmission for a vehicle, there is conventionally known a continuously variable transmission (CVT) that can continuously change the speed ratio. In the vehicle equipped with the CVT, when the vehicle travels at a constant low vehicle speed in the state where an engine is operated in a low-rotation medium-load range, the CVT is controlled to maintain the output of the engine at a constant rotational speed. In this travel state, the driving force of the vehicle and the travel resistance of the vehicle are balanced, so that various components (fitting portions between a clutch drum and a separator, between a core plate and a hub, between a primary sheave and a carrier, etc.) of the CVT tend to be in a floating state.
In order to continue to travel at the constant low vehicle speed in the state where the engine is in the low-rotation medium-load range, the burning rate of fuel in the engine needs to be increased, but, then, rotation fluctuation and torque fluctuation tend to occur in the output of the engine. When these fluctuations are input to the CVT in the floating state, rattling noise occurs at the various components that are in the floating state.
As a conventional technique for suppressing the occurrence of rattling noise, for example, in Japanese Patent Application Publication No. 2015-214260 (JP 2015-214260 A), it is determined whether or not the state of a vehicle satisfies a rattling noise occurrence condition, and when the condition is satisfied, a CVT is controlled to increase the rotational speed of an engine so as to deviate the operating state of the engine from a low-rotation medium-load range, thereby suppressing the occurrence of rattling noise.